Effect of the trifluoromethyl group on torquoselectivity in the 4π ring-opening reaction of oxetenes: stereoselective synthesis of tetrasubstituted olefins

2014 ◽  
Vol 5 (1) ◽  
pp. 410-415 ◽  
Author(s):  
Kohsuke Aikawa ◽  
Natsumi Shimizu ◽  
Kazuya Honda ◽  
Yūta Hioki ◽  
Koichi Mikami
Keyword(s):  
Ring Opening ◽  
Stereoselective Synthesis ◽  
Trifluoromethyl Group ◽  
Ring Opening Reaction ◽  
Tetrasubstituted Olefins

Torque control by metal-orbital interactions

2006 ◽  
Vol 78 (2) ◽  
pp. 415-423 ◽  
Author(s):  
Masahiro Murakami ◽  
Yasufumi Miyamoto ◽  
Munehiro Hasegawa ◽  
Ippei Usui ◽  
Takanori Matsuda
Keyword(s):  
Transition State ◽  
Ring Opening ◽  
Stereoselective Synthesis ◽  
Torque Control ◽  
Orbital Interactions ◽  
Silicon Carbon ◽  
Highest Occupied Molecular Orbital ◽  
Ring Opening Reaction ◽  
Novel Method ◽  
Metal Orbital

The silyl substituent of 3-silylcyclobutene prefers inward rotation rather than outward rotation during a thermal ring-opening reaction, giving the Z-isomer predominantly. This intriguing behavior was explained by assuming electron-accepting interactions between the low-lying σ*-orbital of the silicon-carbon linkage and the highest occupied molecular orbital (HOMO) of the opening cyclobutene system, which are possible only in the inward transition state. On the basis of this finding, a novel method for the stereoselective synthesis of functionalized 1,3-butadiene derivatives from cyclobutenones was developed. Boryl substituents exhibit even stronger preference for inward rotation than silyl substituents as a result of electron delocalization from the cyclobutene HOMO into the vacant p-orbital of boron at the inward transition state.

Enantioselective ring opening of tropinone. A new entry into tropane alkaloids

1997 ◽  
Vol 75 (6) ◽  
pp. 754-761 ◽  
Author(s):  
Marek Majewski ◽  
Ryszard Lazny ◽  
Agnieszka Ulaczyk
Keyword(s):  
Ring Opening ◽  
Stereoselective Synthesis ◽  
Tropane Alkaloids ◽  
Amine Hydrochloride ◽  
Lithium Amides ◽  
Ring Opening Reaction ◽  
Alkyl Chloroformates ◽  
Optically Pure ◽  
Enantioselective Deprotonation

The lithium enolate of tropinone reacts with alkyl chloroformates to give 6-N-carboalkoxy-N-methyl-2-cycloheptenones (4). These compounds can be produced enantioselectively, in up to 95% ee, if chiral lithium amides (derived from optically pure amines 5–7) are used for deprotonation of tropinone in the presence of additives. The effect of additives such as LiCl, LiBr, LiF, LiClO4, CeCl3, ZnCl2, LiOH, TMEDA, HMPA, and DMPU on enantioselectivity of this deprotonation–ring opening sequence varies from slight to very large depending on the chiral amide – additive combination. Especially large increases in enantioselectivity are observed when the chiral, C2 symmetrical, lithium bis-α,α′-methylbenzylamide (Li-5a) is used with one equivalent of LiCl. This reagent is best generated in situ from the corresponding amine hydrochloride and n-BuLi (2 equiv.). The ring-opening reaction combined with transposition of the carbonyl group (via Wharton reaction or allylic oxidation) provides a new method of stereoselective synthesis of tropane alkaloids having a protected hydroxyl at C-6 or C-7 (6β- and 7β-acetoxytropanes 14a, b) and physoperuvine (19). Keywords: enantioselective deprotonation, tropane alkaloids.

Regio- and Stereoselective Synthesis of a Novel Family of Unsaturated Compounds with the S–Se Bond and Their Cyclization to 2,3-Dihydro-1,4-thiaselenines

Synthesis ◽  
2019 ◽  
Vol 51 (08) ◽  
pp. 1832-1840 ◽  
Author(s):  
Svetlana Amosova ◽  
Andrey Filippov ◽  
Vladimir Potapov ◽  
Maxim Penzik ◽  
Nataliya Makhaeva ◽  
...  
Keyword(s):  
Ring Opening ◽  
Room Temperature ◽  
Stereoselective Synthesis ◽  
Reaction Times ◽  
Nucleophilic Attack ◽  
Selenium Atom ◽  
Efficient Synthesis ◽  
Reaction Conditions ◽  
Ring Opening Reaction ◽  
Acid Catalyzed

Regio- and stereoselective ring-opening reaction of 2-bromomethyl-1,3-thiaselenole with thiols proceeded as nucleophilic attack at the selenium atom of seleniranium intermediate affording unsaturated selanyl sulfides, (Z)-CH2=CHSCH=CHSeSR, in up to 93% yield. Dithiols were involved in this reaction giving symmetrical polyunsaturated compounds with two S–Se bonds in 70–75% yields. Efficient synthesis of 2-(organylsulfanyl)-2,3-dihydro-1,4-thiaselenines in 69–96% yields was developed by the acid-catalyzed cyclization of the unsaturated selanyl sulfides. Mild reaction conditions (room temperature) and short reaction times are important features of this methodology.

Synthetic Studies on Cyclocitrinol: Construction of the ABC Ring System Based on Epoxy-Nitrile Cyclization

Synlett ◽  
2020 ◽  
Author(s):  
Kazuto Sato ◽  
Keiji Tanino
Keyword(s):  
Intramolecular Cyclization ◽  
Ring Opening ◽  
Model Compound ◽  
Stereoselective Synthesis ◽  
Ring System ◽  
Cyclization Reaction ◽  
Ring Opening Reaction ◽  
Synthetic Studies ◽  
Highly Strained

The stereoselective synthesis of a model compound containing the ABC ring system of cyclocitrinol was accomplished. After connecting a C-ring allyltitanium segment with an A ring bicyclo[4.1.0]heptanone segment, the seven-membered B ring moiety was constructed by an intramolecular cyclization reaction of an epoxy nitrile. The enone moiety was introduced through an oxidative decyanation reaction, and the bicyclo[4.4.1]undecane skeleton with the highly strained olefin moiety was formed through a ring-opening reaction of the bicyclo[4.1.0]heptane substructure.

On the Conrotatory Ring Opening of 3-Carbomethoxycyclobutene Vis-À-Vis 3-Carbomethoxy-1,2-Benzocyclobutene and the Predominant Inward Opening of 3-Dimethylaminocarbonyl-1,2-Benzocyclobutene

2018 ◽  
Author(s):  
Veejendra Yadav ◽  
Dasari L V K Prasad ◽  
Arpita Yadav ◽  
Maddali L N Rao
Keyword(s):  
Transition State ◽  
Ring Opening ◽  
Electron Process ◽  
Ring Opening Reaction ◽  
Stable Species ◽  
Electron Event

<p>The torquoselectivity of conrotatory ring opening of 3-carbomethoxycyclobutene is controlled by p<sub>C1C2</sub>→s*<sub>C3C4</sub> and s<sub>C3C4</sub>→p*<sub>CO</sub> interactions in the transition state in a 4-electron process as opposed to only s<sub>C3C4</sub>→p*<sub>CO</sub> interaction in an apparently 8-electron event in 3-carbomethoxy-1,2-benzocyclobutene. The ring opening of 3-carbomethoxy-1,2-benzocyclobutene is sufficiently endothermic. We therefore argue that the reverse ring closing reaction is faster than the forward ring opening reaction and, thus, it establishes an equilibrium between the two and subsequently allows formation of the more stable species <i>via</i> outward ring opening reaction. Application of this argument to 3-dimethylaminocarbonyl-1,2-benzocyclobutene explains the predominantly observed inward opening.</p>

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